When you achieve a respectable Grimoire score of at least 2200. Grimoire does not reflect on skill but it does say that one has put effort into the game and should have experienced Destiny's hardest game modes on numerous occasions. Sometimes, this is not always the case. Take Crota's End Bridge CP for example. Imagine you had a skilled player but inexperienced. His inexperience could potentially cause an Annihilator wipe as it takes more than skill to do that section legit.